<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
	.box1,.box2,.box3 {
		float: left;
	}
		.box2 {
			width: 200px;
			background-color: pink;
			margin-left: -100%;
		}
		.box1 {
			width: 100%;
			background-color: purple;
		}
		.box3 {
			width: 200px;
			background-color: blue;
			margin-left: -200px;
		}
		.box4 {
			margin: 0 200px;
		}
	</style>
</head>
<body>
	<div class="box1">
		<div class="box4">内容</div>
	</div>	
	<div class="box2">首页</div>
	<div class="box3">内容</div>
</body>
</html>